[t.ellingham]

Going over past papers and having problems with this question.

"A boiler heats high pressure water from 80C to 152C and then evaporates it without raising the temperature. The specific heat capacity is 4.86 kJ/kg K and the latent heat Ufg is 1923 kJ/kg. Calculate the change in internal energy of 1 kg."

Would be greatful if somone could give me some advice or show me how they would answer it.

thanks

[mmneedtokill]

You need to use m c delta t + ufg

[t.ellingham]

(Original post by mmneedtokill)
You need to use m c delta t + ufg

1kg x 4.86 x 72 + 1923 = 2271.92

Is this anywhere close?

[Ari Ben Canaan]

(Original post by t.ellingham)
1kg x 4.86 x 72 + 1923 = 2271.92

Is this anywhere close?

Typo. It should be 720

[t.ellingham]

(Original post by Ari Ben Canaan)
Typo. It should be 720

sorry, tsr converted the degrees sign into a 0, the values are actually, 80C and 152C

is my answer at all right?

[t.ellingham]

(Original post by Ari Ben Canaan)
Typo. It should be 720

is my answer right if i use 72?

[Ari Ben Canaan]

(Original post by t.ellingham)
is my answer right if i use 72?

I suspect so unless I'm missing something..

[mmneedtokill]

(Original post by t.ellingham)
1kg x 4.86 x 72 + 1923 = 2271.92

Is this anywhere close?

Your formula is correct but answer is wrong.
Your current answer is in kj/s but I'd convert it to MW

[t.ellingham]

(Original post by mmneedtokill)
Your formula is correct but answer is wrong.
Your current answer is in kj/s but I'd convert it to MW

if i convert it to MW, giving me 2.27 MW. would this be the correct answer?

thanks for your help

[Ari Ben Canaan]

(Original post by t.ellingham)
if i convert it to MW, giving me 2.27 MW. would this be the correct answer?

thanks for your help

The other user is wrong. You cannot convert your answer to watts as internal energy is measured in JOULES not J/s.

That is, internal energy is NOT a measure of power.

Keep it in joules or KJ....